The present invention relates to a molten mix process for making bar compositions comprising synthetic anionic surfactant and fatty acid which process allows higher quantities of essentially water soluble soap (e.g., soap having solubility equal to or greater than 82/18 tallow coconut soap) to be used than previously thought possible while enhancing bar finishing properties. Using a molten mix process, ingredients are mixed at temperatures above about 110xc2x0 F. before the molten composition is chilled, optionally refined and/or milled, plodded to extrudate (generally in form of extruded xe2x80x9clogsxe2x80x9d) and cut and stamped into final bars. In these molten mix processes, higher soluble soap levels are associated with materials becoming soft and sticky and causing finishing problems, especially those related to bar stamping. The process of the invention comprises a modification of the process to avoid the noted finishing problems.
It is well known to make extruded bar compositions using synthetic anionics (e.g., acyl isethionates, alkyl glyceryl ether sulfates etc.) and fatty acid soap.
The soap in such compositions is generally known to serve a number of purposes. First, it serves to help structure the bars so it does not readily crumble both when the bar is being xe2x80x9cfinishedxe2x80x9d (e.g., extruded, stamped) and also as a final user bar. Fatty acid soap also provides some beneficial user properties such as good lather and a certain skin feel which may be desirable to some consumers. In addition, soap is generally cheaper than most anionics and provides some cost savings.
Despite the advantages noted above, however, the level of soap which can be used in the process for making these bars (e.g., molten process in which ingredients are mixed at a temperature above about 110xc2x0 F.) has generally been considered to have a cap because excessive levels lead to poor bar finishing properties (e.g. principally in that the bars are stickier and result in problems in bar extrusion and stamping when these stickier bars stick to the machinery). Thus, in a bar typically containing 30-75% anionic, preferably 35 to 60% anionic, levels of soap above 5% can lead to the above noted finishing problems.
Without wishing to be bound by theory, at least part of this problem is believed to be due to the fact that increasing soap levels generates soap solutions and/or isotropic liquid crystal phases with unbound water within the synthetic detergent (syndet) bar formulation. The presence of such phases have the potential to hinder the finishing stages of production, which includes extrusion and stamping, by rendering the material soft and sticky.
Unexpectedly, applicants have found that if a source of divalent cation is provided such that the divalent cation is made available to the mix solution (e.g., to be made available, the source component must have solubility equal to or greater than that of calcium carbonate); and sufficient divalent cation is made available to react with the soluble soap dissolved in the unbound water, the degree of softness and stickiness during final bar production can be lessened or alleviated.
U.S. Pat. No. 5,981,451 to Farrell et al. relates to a process for making bars containing a mixture of anionic surfactant and soap, but there the process is a non-molten process and stickiness issues of finishing a bar are primarily encountered when using a molten mix process.
U.S. Pat. No. 4,557,853 to Collins relates to bars containing alkaline earth metal carbonates as skin feel agents. Given the low water solubility of these carbonates, it is believed that the level used (2.4 to 5.9% earth metal carbonate as defined by the surfactant to earth metal carbonate ratio) is too low to provide a sufficient amount of divalent ion to control the level of soluble soap in solution. That is, the patent fails to recognize the link between providing available divalent cation which can insolubilize the soap at a certain point in the process and thereby reduce stickiness during the finishing stages of bar processing. It should also be noted that the finishing process is considerably less likely to suffer from soft, sticky material issues when soap is the predominant constituent of the formulation.
WO 95/13356 to Procter and Gamble relates to an acyl isethionate bar containing liquid polyols and magnesium soap. Bars made by the process of the subject invention do not require liquid polyols of this reference. (However unnecessary the use of liquid polyols in subject invention, it should be noted that the inventors of the subject invention do not wish to exclude possibility of using liquid polyols in formulations). Moreover, the patent does not recognize the need for providing available/excess divalent cations (e.g., to aid as scavengers for otherwise soluble soap during molten mixing where, if not removed, they are believed to be the cause of down stream xe2x80x9cfinishingxe2x80x9d problems) and, on the contrary, requires the initially used magnesium soap to stay bound and to act as a filler process aid.
More particularly, the subject invention comprises a process for making a bar comprising:
(1) 20% to 75%, preferably 35% to 60% by wt. of an anionic surfactant, preferably alkali metal salt of alkyl isethionate;
(2) about 4% to 20%, more preferably 6% to 12% of a fatty acid soap or soap fraction having solubility equal to or greater than 82/18 tallow/coconut soap (i.e., solubility of 1.1 g/l in water at 40xc2x0 C.);
(3) 4% to 30%, preferably 10% to 25% free fatty acid; and
(4) compound or compounds which is a source of divalent cation; which process comprises mixing components (1), (2) and (3) and a compound or compounds which is a source of divalent cation (4) and which compound (4) is used in an amount sufficient that, when the divalent source compound is solubilized, it provides sufficient available cation to interact with soluble soap and thereby increase throughput 10% to 200% (assuming other variables are exactly same or substantially similar), said throughput being defined by greater extrusion rate and or greater number of bars stamped per minute.
The solubility of the divalent cation source may affect the amount of the compound used in the process. Thus, it should be understood, for example, that more calcium carbonate may be needed because the solubility of calcium carbonate is low while, for a more soluble salt such as magnesium or calcium chloride, much greater amounts may be required.